Friday, December 2, 2011

Engineering Drums Part Seven: Overheads

While the kick and snare microphones carry the bulk of the responsibility in pop music mixes, the overall image and presence of the drum kit is defined by the overhead microphones. Not only do the overhead mics pick up the cymbals, they also pick up different perspectives of the snare and toms – even the kick. These mics, however, are many times the distance from each drum than that drum's own mic, so any potential phase issues are eliminated, that is, the distant sound of the drums as captured by the overhead mics is so radically different in content than the sound picked up by the close mics that when combined the two compliment rather than fight one another.

Overheads often help to define the sense of space around the kit as well, particularly if the drums are being tracked in an ambient room.

In a very real sense the sound of the kit picked up by the overheads is the glue that make all the various elements of the kit belong together in the mix. It is for this reason that we don't try to isolate the cymbals from the kit (which I strongly discouraged in Part Three).

Overwhelmingly, condenser mics are chosen for overheads. Condensers reproduce high frequencies and intimate detail better than other types of mics. Both small and large diaphragm condensers are commonly used. Small diaphragm models have a faster impulse response that sounds truer to life, while large diaphragms, with their greater mass, tend to produce a sound that is smoother and bigger.

Let's talk briefly about polar patterns. By far the most common pattern used for miking drums is cardioid. The directionality of the cardioid pattern makes it a good choice for better isolation when using so many mics in such a small area. When used for overheads cardioid mics give the engineer the ability to create a dramatic stereo image of the drumkit.

The omnidirectional pattern, by contrast, doesn't discriminate against sound coming from any particular direction, but rather, picks up all sound, regardless of where it's coming from. A pair of omnis, a couple of feet off the cymbals and spaced a few feet apart can yield an incredibly natural stereo image (which I personally enjoy), but this arrangement will also pick up more of the room the drums are in than a cardioid pair will. Because they don't reject sound from any particular direction, omnis hear much more of the environment around the drums, so while they can produce wonderful results, they also require a bit more effort to capture the balance you want.

Let's start with cardioids. For a good balance place the mics a couple of feet above the cymbals, one on each side of the kit, separated 4-5 feet, pointing essentially straight down. The spacing of this approach, coupled with the directional characteristics of the mics creates a sufficiently wide, yet natural image of the overall kit.

To ensure a solid snare drum image take care to position the diaphragms of both mics the same distance from the center of the snare drum head. The snare is arguably the most critical drum on the set, and is clearly captured by the overheads. With the overhead mics equidistant from the snare, the snare sound will arrive at each mic simultaneously which will avoid the head-spinning phasiness that can easily occur when the mics are unequally placed. Because the snare drum is to the side of the kick drum spacing the overheads equidistant from its center usually means one of the mics will be placed higher off the ground than another (assuming you keep the mics directly over the cymbals). Don't let this concern you.

For greater stereo separation angle the mics away from each other toward the outer edge of the kit. For less separation bring the mics physically closer together, remembering to keep their spacing equidistant from the center of the snare drum.

Another common approach for overhead placement, which provides a more natural, subtle stereo image is to center a pair of cardioid condensers over the kit, with their capsules almost touching, pointed 45-55 degrees off axis (for a total angle of about 90-110 degrees) toward the edges of the kit. Because the mics are so close together the sound of everything on the kit practically hits each mic at the same time, eliminating phasing for just about every part of the kit, and the directionality of the mics provides the separation. Off-axis coloration from each mic blends the middle information smoothly, creating a more natural perspective.

If you want more sound from the room you can switch to omnidirectional mics, or you can raise cardioid mics higher into the air, providing more space for room reflections in the sound.

Hi-hats will often get their own mic, usually a cardioid condenser, placed about a foot off the top of the pair. Point the mic toward the center of the top cymbal for a more focused sound, and toward the edge for a more aggressive character. Place the mic in such a way as to point away from the kit, while pointing at the hi-hats. This will help isolate the hats from the rest of the kit.

On occasion the ride cymbal will also gets its own mic, also a cardioid condenser, placed similarly as the hi-hat mic, or, occasionally, underneath the ride. The 3-to-1 rule applies here, that is, the overhead mics should be at least 3 times as far from the ride as the ride mic to avoid phasing when the ride is played. Take care not to place it too close to the ride. Most rides are large and heavy and create a great deal of hummmmm..... so stay far enough away to keep it sounding like a proper ride cymbal.

By miking hi-hats and rides separately it gives the mix engineer more control over the definition of these time-keeping elements in the groove.